In an air-conditioning apparatus established by connecting a plurality of use units to at least one heat source unit via refrigerant extension pipes, a refrigerant is charged at the time of installation work of the units with the amount according to the length of the refrigerant extension pipes at the installation site. Here, if the charged refrigerant amount is not adequate, a flaw in the operating state of the air-conditioning apparatus will occur. If there is an overcharge, for example, the pressure in the refrigeration cycle apparatus during operation of the device will be high; hence, the device will be forced to be stopped due to safety reasons and will fall into a situation not allowing its operation to be performed. Conversely, if the charged refrigerant amount is insufficient, the intended cooling capacity and the heating capacity cannot be obtained. Accordingly, technological development for charging adequate amount of refrigerant in the air-conditioning apparatus has been conventionally made (see, Patent Literature 1, for example).
In the air-conditioning apparatus described in Patent Literature 1, the optimum refrigerant amount as a target charging value for the heat source unit and the use units are obtained in advance through experiments and simulations. Further, an automatic refrigerant charge operation is carried out such that refrigerant charging is carried out until the total value of the refrigerant amount in the heat source unit and the refrigerant amount in the use units, which are computed from the refrigerant flowing in the refrigerant circuit or the operation state quantity of the components, reach the target charging value. With this method, it will be possible to carry out automatic charging of the refrigerant even if the pipe length of the refrigerant communication pipe is unknown, since it only requires computation of the refrigerant amount of only the heat source unit and the use units.
Further, as a technique for calculating the refrigerant amount in the air-conditioning apparatus, there is one described in Patent Literature 2. In Patent Literature 2, a method is disclosed in which an internal volume of a refrigerant extension pipe is computed from operation data and an initial charge amount so as to compute the refrigerant amount, regardless of the difference in the pipe length of the refrigerant extension pipe that corresponds with the installation condition at the installation site. Further, in Patent Literature 2, a method is disclosed in which the internal volume of the refrigerant extension pipe is computed using two or more different sets of operation data such as operation data of different liquid refrigerant extension pipe temperatures when the initial charging amount is unknown.